DESCRIPTION (prepared by applicant): The investigators propose to develop a systematic approach to evaluating near continuous glucose sensors in children and adolescents. This approach can be used in the assessment of current sensors now available to the public, and for future sensors that become available during this project. Accuracy will be determined using normal controls and children with diabetes. Initial accuracy measurements will be performed in a CRC using a laboratory quality measurement of glucose. The sensors will then be assessed in the home environment to determine their usefulness in detecting changes in blood glucose levels and improving diabetes management. The investigators will collect detailed record of food intake, and a continuous record of physical activity will be obtained using an accelerometer as well as psychological assessments. These data will be integrated to evaluate the multiple factors leading to hypoglycemia and variability in blood glucose levels, as well as provide effective tools for improving diabetes management. In the future these data will be valuable in developing algorithms that incorporate this information into a closed loop insulin delivery system. Aim 1 is to determine the accuracy of near-continuous glucose monitors in normal children. This will allow assessment of the possible physiologic effects, such as sleep and physical activity on glucose levels. These studies will also allow determination of the incidence of sensor readings in the hypoglycemic range despite normal blood glucose levels. Aim 2 is to determine the accuracy of near-continuous glucose sensors in children with diabetes. Particular attention will be given to the detection of hypoglycemia, especially nocturnal hypoglycemia, and the accuracy of sensors during physical activity. Aim 3 is to assess hypoglycemia in a contemporaneous population of children with Type 1 diabetes using near continuous glucose monitoring. This will be an observational study in a home environment. Aim 4 is to assess the long-term effectiveness of near continuous glucose monitoring on decreasing the frequency and severity of hypoglycemic reactions, and improving glycemic control.